The invention relates to a formwork system for prefabricated concrete parts, having a magnetic body, which can be placed with its underside on a base plate, and on which the formwork parts are to be fixed in their respective position, wherein the formwork part has a lift-off stirrup engaging over the magnetic body, and there is a gap between the stirrup and the cover side of the magnetic body facing away from the base place, into which gap the magnetic body can be drawn via a lifting element.
Such a formwork system is known, for example, from European Patent EP-0 842 339 B1. There a formwork system is described, in which the lifting element is formed by a lifting rod, which is permanently braced on the lift-off stirrup by the interposition of a spring. Such springs must be exactly adjusted to the respective application case, which represents a certain expense. If a magnetic body is not properly lowered, the springs described there can also bring about its relifting.
An object of the present invention is accordingly to further develop a formwork system of this type such that, on the one hand, a lower expenditure is necessary in designing the system and on the other hand, the effect of an unintentional, automatic relifting no longer occurs. In sum, the operating safety of the system overall should thereby be improved.
This objective is accomplished according to the invention, in that retaining elements are present, which are to be releasably coupled to the magnetic body when this is drawn into the slot.
The invention has the advantage that, by the releasable retaining elements, the magnetic body in its retracted state is fixed securely in the lift-off stirrup without spring elements being necessary for this. But due to the releasability, it is at the same time assured that the magnetic bodies can again be securely placed on the base plate.
It is advantageous if the coupling of the retaining elements in their raised state takes place automatically, wherein particularly the coupling while overcoming a pressure point offers the advantage that a tangible feedback about a successful secure raising and coupling is communicated to an operator.
Basically, the forces applicable here from the coupled retaining element to the raised magnetic body should be greater that its own weight, so as to guarantee that, after raising the magnetic body and coupling it, the formwork can be securely handled without major problems.
A possible coupling element is represented by magnets and adhesion surfaces, which are arranged in the area of the gap between magnetic body and lift-off stirrup. The magnets can here be integrated into the magnetic body, but in particular also be formed by its cover side. In order to restrict the coupling force, the adhesion surface has a smaller planar extension than the cover side.
One possibility for restricting the planar extension of the adhesion surface is to use for this the front face of web plates arranged in the slot. These are in total so small in their dimensions, that the danger does not even exist that a foreign object, for example a small stone or the like, would get between the adhesion surface and magnetic bodies, which would impede coupling.
With other types of coupling elements, it is a question of spring means hooking in under a rebound, wherein these in particular engage the lifting element. Here, for example, it is a matter of a springy latching element, which engages into a corresponding latching groove on the lifting element and then fixes this in the raised position. It is also conceivable, however, to allow appropriate spring elements to engage directly on the magnetic body, whereby it is possible, for example, to draw the magnetic body over, for example, projections situated on the side walls of the lift-off stirrup.
Projections of this type can instead be provided on a guide running around the magnetic body inside the lift-off stirrup, wherein such a guide is to be used particularly when the lift-off stirrup is integrated into a formwork part and the width of a magnetic body is smaller than the width of the formwork system. In such cases, a greater free space is granted to the builder in designing the formwork with the guide, which is adapted to the magnetic body in its free width. A guide of this type can advantageously also even have a stripping edge facing the magnetic body, by which concrete or the like adhering to the magnetic body is to be stripped off, so that the magnetic body is continuously cleaned, and the formwork system consequently requires less maintenance.
Here a slight play is provided between the magnetic body and the stripping edge, so that the magnetic body cannot tilt and jam inside the guide between stripping edges.
Advantageously the guide is constructed overall such that it forms with the lift-off stirrup a substantially closed space, into which the magnet is to be raised. This substantially closed space is likewise advantageous or requires little maintenance for the formwork system.